Motor disorders have long been known to follow damage to the dorsal columns. However, following extensive postoperative training, the only enduring deficits are those involving the grasping and manipulation of objects with the fingers. These results have indicated that the dorsal columns provide specialized sensory information that is critical to the execution of the precise finger movements involved in active touch. As a source of feedback to motor cortex, the dorsal columns may provide information that is critical for digital fractionation, involving precisely timed and directed sequences of movement of individual digits. The proposed experiments test this hypothesis with a methodology that permits direct challanges and measurements of digital motor acts. We have developed two paradigms which evaluate the ability of monkeys to make independent finger movements or track moving stimuli with the fingers. The experiments will evaluate in detail the deficits in individual finger movements that result from DC lesions, and the animals will be retrained to maximal capacity with specialized shaping procedures. The contributions of separate populations of joint and cutaneous receptors to digital fractionation and tracking will be evaluated, and the role of dorsolateral sensory pathways in recovery of digital dexterity will be determined. Because the corticospinal pathway is regarded as the afferent pathway of control over motoneurons involved in digital fractionation of primates, the consequences of dorsal column and corticospinal tract section will be compared directly. A major goal of this work is to provide information of direct relevance to clinical neurology and neurosurgery. A better understanding of spinal tract function is fundamental to accurate diagnosis of CNS pathology affecting the somatosensory system. Also, fundamental to an understanding of somatosensory coding mechanisms at thalamic and cortical levels is an accurate description of the functional contributions of the different spinal inputs to these regions. We have previously demonstrated that many of the initially debilitating motor effects of DC lesions recover with training. Fine movements of the hands have been an exception to this, but training procedures are critically important in providing the full opportunity for recovery. The stepwise shaping procedures for the finger movement tasks are appropriate to test the limits of functional plasticity of the spinal cord following well-defined damage.